Because of the general use of central air heating and cooling systems, we have come to believe that our indoor thermal comfort depends mainly on air temperature.
Experts have said that thermostats across the world are often fixed at 22 degrees — which, they argue, is costing the economy billions of dollars and pumping hundreds of thousands of tonnes of unnecessary carbon into the atmosphere. If we all stuck to the 19C and 25C rule, Australian businesses could save $100 million and 300,000 tonnes of carbon every year, they argue.
“The built environment is heated and cooled to a fixed 22 degrees regardless of the temperature outside temperature”. See http://www.news.com.au/finance/money/costs/setting-your-air-con-to-25c-in-summer-could-save-billions/news-story/988852285c91683b3a869db3446fbf50
Changing thermostat settings is a great way to save energy, but with forced air systems (convective systems) this may result in a compromise of indoor comfort.
The advantages of Radiant Heating and Cooling
However, the human body exchanges heat with its environment not only through convection, but also radiation, conduction and evaporation. Convection relates to the heat exchange between the skin and the surrounding air (used by normal air con), radiation is the heat exchange between the skin and the surrounding surfaces, evaporation concerns the moisture loss from the skin, and conduction relates to the heat exchange between a part of the human body and another object that it’s in contact with.
Radiant Heating- how it works to keep you warmer
In winter we can remain comfortable in lower air temperatures by increasing the share of radiation or conduction in the total heat transfer of a space by using underfloor hydronic heating. Radiant heat can keep people comfortable at a lower air temperature.
The obvious example of radiant heating is direct sunlight. In spring or autumn, we can sit comfortably outside in the sun wearing only a T-shirt, even if the air temperature is relatively low. A metre away, in the shade, it can be cold enough to need a jacket, although the air temperature is more or less the same. In summer, we prefer the shade as it screens excessive radiant heat.
The difference is explained by the radiant energy of the sun, which heats the body directly when it is exposed to sunlight. The use of radiant underfloor heating creates a higher "radiant temperature", allowing thermal comfort at a colder air temperature in winter, reducing the energy costs required for heating.
That’s why a radiant underfloor heating system can create very comfortable indoor air temperatures in winter with the wall thermostat set a couple of degrees lower (19C) than an equivalent size forced air heating system (22C).
Radiant Cooling -how it works to keep you cooler
The opposite is also true: The human body is an exothermic heat generator. Heat emission from the body occurs via Radiation (~45%)- Convection (~30%) - Evaporation (~20%) - Conduction (~5%). Our bodies radiate heat to any surface in line of sight that is cooler than our own body surface temperature of about 30-32C. Therefor a floor cooling system can increase radiant heat loss and increase human comfort even if the room air temperature is higher than normal. For example, a person standing in a room with radiant cooling will feel comfortable even if the air temperature is 25ºC, whereas forced air cooling is often set at 22C. This is because the body loses heat to the floor through radiation and conduction. The result is less energy required for the same level of comfort in the room.
A cooler Mean Radiant Temperature increases the radiant heat loss from the human body to the surfaces that are cooler with radiant cooling. Radiant cooling allows a higher space set-point temperature, while still maintaining the same level of cooling comfort compared to a traditional air handling unit (AHU) loads can be reduced to use 24 to 25°C vs. 22°C indoor design temperature with radiant cooling in most cases.
- Indoor air does not have to be so cool for comfort
- Indoor air can be warmer, reducing air volume, noise, drafts, etc.
Using the superior heat transfer properties of water compared to air allows the hydronic portion of the system to efficiently distribute energy to conditioned spaces. For example a 60 watt water circulator pump can deliver the same energy as a 1,500 watt air distribution fan.
Smart control technology
Modern radiant heating and cooling systems therefore are proven to provide the same level of comfort as air conditioning systems at a lower energy cost. However they can save even more energy when managed by modern electronic controls that reduce energy even more when not required. Smart controls will automatically manage the zones that require heating and cooling to match the occupancy of the residence. For example they have settings for 4 time periods in the day;
Heating in winter
- Morning before work or school – 6 to 8am – set temp 21C
- At school or work during the day – 8am to 4pm – set temp 19c
- Home in the evening 4pm to 10pm – set temp 21c
- Bed time - 10pm to 6am – set temp 17c
Cooling in Summer
- Constant temperature = 24C
Radiant floor heating and cooling systems combined with smart control technology have been proven to reduce up to 50% of the operating costs of conventional air conditioning systems with improved indoor comfort, providing long terms energy cost savings and lower maintenance.